The present invention relates generally to formaldehyde free binders for use in the glass fiber manufacturing process, and more particularly, to a formaldehyde free co-binder solution formed by using a polyol to crosslink polyacrylic acid and a polyacid monomer or oligomer.
Phenol-formaldehyde binders have been widely used to treat fiberglass since they have a low viscosity in the uncured state, yet form a rigid thermoset polymeric matrix for the glass fibers when cured. A low binder viscosity in the uncured state is required to allow the maximum vertical expansion of the coated mat when it exits the forming chamber. A binder which forms a rigid matrix when cured is required so that a finished fibrous glass thermal or acoustical insulation product, when compressed for packaging and shipping, will recover to its as-made vertical dimension when installed in a building.
The phenol/formaldehyde binder utilized in the past have typically been the highly alkaline resole type which have the combined advantages of inexpensive manufacture and water solubility. The binders are applied to the fiberglass from aqueous solution shortly after the fibers have been produced, and cured at elevated temperature in a curing oven. Under the curing conditions, any remaining aqueous solvent is evaporated, and the phenol/formaldehyde resole cures to a thermoset state. The fibers in the resulting fiberglass product are thus partially coated with a thin layer of thermoset resin, which tends to accumulate at the junctions where fibers cross each other. The resulting product therefore not only suffers from less self-abrasion, but also exhibits higher recovery than a fiberglass product not incorporating a binder.
The alkaline phenol/formaldehyde resoles contain a fairly large excess of formaldehyde from the manufacturing process. This excess of formaldehyde has been taken advantage of by adding urea to the phenol/formaldehyde resole, resulting in a urea-extended resole. Urea-extended phenol/formaldehyde binders are more cost-effective than the straight phenol/formaldehyde resins, but exhibit some loss in properties as the urea content increases. Thus, efforts have been made to incorporate other resins which can enhance the properties of the binder.
In particular, insulation manufacturers have long desired an alternative polymeric binder system for fibrous glass products. However, low molecular weight, low viscosity binders which allow maximum vertical expansion of the mat in the transfer zone generally cure to form a non-rigid plastic matrix in the finished product, thereby reducing the attainable vertical height recovery of the finished insulation product when installed. Conversely, high viscosity binders which generally cure to form a rigid matrix in the finished product do not allow maximum vertical expansion of the coated, uncured mat. Therefore, it is desirable to prepare a non-phenol/formaldehyde binder having a low viscosity when uncured and structural rigidity when cured.
Accordingly, an important object of the present invention is to provide a formaldehyde free co-binder solution that has a low viscosity before curing and structural rigidity after curing.
It is another object of the present invention to provide a formaldehyde free co-binder solution that is formed by using a polyol to crosslink polyacrylic acid and polyacid monomer or oligomers.
It is yet another object of the invention to provide formaldehyde free co-binder solutions that have a reduced molecular weight and reduced viscosity.
It is a feature of the present invention that the formaldehyde free binder solutions are cross-linked.
It is an advantage of the present invention that the amount of polycarboxylic acid used in the co-binder solution is reduced over conventional binder solutions, thereby reducing cost.
It is another advantage of the present invention that there is minimal precure of the co-binder solution on the glass fiber.
These and other objects, features, and advantages are accomplished according to the present invention by providing a method of forming a formaldehyde free co-binder solution that includes admixing a polyacid monomer or oligomer having at least two carboxylic acids and a molecular weight of 1000 or less and a polyol having at least two hydroxyl groups with agitation for a period of time sufficient for said polyacid monomer or oligomer and said polyol to react and form a reaction product. A polycarboxylic acid is then added to said reaction product to form a substantially crosslinked co-binder solution having a reduced viscosity and cure temperature.
The foregoing and other objects, features, and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description that follows, in conjunction with the accompanying sheets of drawings. It is to be expressly understood, however, that the drawings are for illustrative purposes and are not to be construed as defining the limits of the invention.